Water Heating System and Valving for These

ABSTRACT

A pump system for use with a solar collector system which is used to heat a heat transfer fluid, includes a storage tank and the pump system having a first and second pump arranged in parallel which can pump the heat transfer fluid from the storage tank to a solar collector, so that should one pump fail the other pump can function, wherein the outlet of the first pump and the outlet of the second pump are connected to a valve arrangement, whereby when the first pump operates the outlet of the second pump is substantially closed by the flow from the first pump and when the second pump operates the outlet of the first pump is substantially closed by the flow from the second pump.

FIELD OF THE INVENTION

The present invention relates to freshwater stations or district waterheating systems, and in particular in improvements to the primarycircuit and the secondary circuit of such systems. More particularly thepresent invention can be used with solar water heating systems, electricboosted solar systems, gas boosted solar systems, cogeneration systemsand hybrid systems.

BACKGROUND OF THE INVENTION

Solar thermal water heating systems with solar panels are subject totemperature and duty cycle events which threaten the integrity of thecollector or its pipes. In the case of freezing temperatures and iceformation, or over-temperature situations where continuing to heat theworking fluid at the collector when there is solar energy absorbed butwhich can no longer be dissipated within the system, resulting in thesuper heating of the working fluid, both situations can causepressurising of the system. In either of these circumstances, onesolution is to drain the solar collector of working fluid and store itin a reservoir for pumping back to the collector or collectors whenneeded. These are known as drain-back systems.

In commercial applications duty standby pumps are often used for pumpskids. When one pump is in operation the other pump is switched off. Inorder to prevent flow from being “short circuited” from one pump to theother, one way valves are installed at the exit of each of theindividual pumps. “Short circuiting” can occur because the type of pumpused is usually a non-positive displacement type, therefore permittingfluid to flow through the pump body even when the impeller is not inoperation. Such systems are not able to use a drain back feature insolar applications, because the installation of one way valves in thecircuit makes backward flow not possible.

Water heating systems that utilise a heat exchanger to separate theworking fluid such as solar or cogeneration systems traditionallycontrol the outlet temperature on the potable water side via a form ofthermostatic mixing valve. The thermostatic mixing valve blends hot andcold water to produce the desired temperature. The valve can be eitherelectronically controlled or via a thermostatic element. When such avalve is used there is an inherent increase in pressure drop across thevalve caused by the pump in the circuit when the valve closes torestrict the flow of hot water. This increase in pressure dropeffectively means the pump is continuing to draw maximum power even intimes where there is little or no load on the system.

A second disadvantage of a valve based system is that, due to the largepressure drop across the valve, large pumps and their associated highcost and power requirements are a necessity.

Any reference herein to known prior art does not, unless the contraryindication appears, constitute an admission that such prior art iscommonly known by those skilled in the art to which the inventionrelates, at the priority date of this application.

SUMMARY OF THE INVENTION

The present invention provides a pump system for use with a solarcollector system which is used to heat a heat transfer fluid, the solarcollector system including a storage tank for the heat transfer fluidused in the solar collector system, the pump system having a first andsecond pump arranged in parallel which can pump the heat transfer fluidfrom the storage tank to a solar collector, so that should one pump failthe other pump can function, wherein the outlet of the first pump andthe outlet of the second pump are connected to a valve arrangement,whereby when the first pump operates, the outlet of the second pump issubstantially closed by the flow from the first pump and when the secondpump operates, the outlet of the first pump is substantially closed bythe flow from the second pump.

The valve arrangement can have three ports and a valve member whicheffectively closes a first pump's outlet port when a second pump isoperating and the first pump is not, and closes the second pump's outletport when a first pump is operating and the second pump is notoperating.

The valve arrangement can have a flap which closes the first pump'soutlet port and moves to a second location when activated by the firstpump to close the second pump's outlet port.

The outlet ports can be located on respective pipes which connect to thepumps.

The pump system can be provided as part of a skid.

The present invention also provides a solar water heating system havinga pump system described above wherein the heat transfer fluid is notpotable water.

The present invention also provides a solar water heating system havinga pump system described above wherein the heat transfer fluid is potablewater.

The present invention further provides a valve for a pump system havingtwo pumps and which will allow drain back of a pumped fluid, the valveincluding a body having first and second ports for respectivelyconnecting to respective pump outlets or conduits from the outlets, anda third port, whereby when a pump is pumping the third port is an outletfrom the body, and when the pumps are not pumping, the third port is aninlet to the body.

Between the first and second ports is located a valve member which canmove so as to close off one of the first or second ports depending uponwhich pump is operating.

The valve member can be a flap.

The flap can be connected by a hinge means to the body which allowsmovement of the flap between the first and the second ports.

The valve member closes off the first or second ports to a substantialextent, that is watertight sealing is not required by the valve.

The flap can be manufactured from a metal, a polymeric material or acomposite material.

Valve seats surrounding the first and second ports can be manufacturedfrom a metal, a polymeric or a composite material.

Surrounding the first port or the second port or the third port is oneof the following: a male thread, a female thread.

Surrounding a respective port is a female thread.

The flap can be held rotatable in the body, or pivotally held in thebody, by means of opposed pins which seal to the body and pass into thebody.

The present invention also provides a water heating system having aprimary circuit to supply a heated heat transfer fluid to a heatexchanger, which supplies heat to a secondary circuit having potablewater therein, wherein the primary circuit includes at least one pump tocirculate the heat transfer fluid through the heat exchanger, and acontrol system to control the operation and output flow rate of at leastone pump, characterized in that the control system measures thetemperature, or an indication of the temperature of the potable waterafter it has left the heat exchanger, so as to control the output flowrate of the at least one pump.

The primary circuit can heat the heat transfer fluid by one of or acombination of more than one of the following: solar; gas, electric,cogeneration means; gas boosted solar; electric boosted solar.

The secondary circuit can have or be one or more of the following: is afreshwater station system; is a district water heating system; a pump; afilter; a cold water supply; an over temperature shut down mechanism.

The water heating system can be such that the heat exchanger is providedin a delivery skid whereby there are two heat exchangers present on theskid, with respective isolation valves and having parallel connectionsto an incoming conduit and an outgoing conduit, whereby one of said heatexchangers is present in a redundancy capacity.

The system can have multiple skids connected to each other to providethe heat exchanger of the system.

The present invention also provides a heat exchanger apparatuscomprising a frame to support at least two heat exchangers, between aninlet conduit and an outlet conduit, wherein the at least two heatexchangers having connection to the inlet and outlet conduit inparallel, the connection being via isolation valves and forming a liquidsupply inlet and heated liquid outlet, and each heat exchanger havingfluid connection, via isolation valves, to a primary circuit to receivea heat transfer fluid to transfer heat to the liquid, characterized inthat at least one of the heat exchangers is present in a redundantcapacity.

The inlet conduit and the outlet conduit have flanged ends to allowconnection to an adjacent like heat exchanger apparatus, and or aconduit closure.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of a preferred embodiment will follow, by way ofexample only, with reference to the accompanying figures of thedrawings, in which:

FIG. 1 illustrates a schematic view of a solar water heating system withprimary and secondary circuits, the primary circuit deriving heatexclusively mainly from solar but is also provided with an electricbooster;

FIG. 2 illustrate a schematic view of a water heating system similar tothat of FIG. 1, except that the system includes a direct gas booster inthe form of a gas boost on the secondary circuit;

FIG. 3 illustrate a schematic view of a water heating system similar tothat of FIG. 1, except that the system includes an indirect booster inthe form of a gas boost on the primary circuit;

FIG. 4 illustrate a schematic view of a water heating system similar tothat of FIG. 1, except that the system is a hybrid system and includesdual indirect boosters in the form of a gas boost and an electric booston the primary circuit;

FIG. 5 illustrate a schematic view of a water heating system, exceptthat the system includes co-generation unit and chiller in the primarycircuit;

FIG. 6 illustrates a perspective view of a flap valve body;

FIG. 7 illustrates a cross section through the valve of FIG. 6;

FIG. 8 illustrates a front view of the valve of FIG. 6;

FIG. 9 illustrates an end view of the valve of FIG. 6;

FIG. 10 illustrates an alternative valve arrangement in the form of aball valve showing operating condition with one pump on;

FIG. 11 illustrates the valve arrangement of FIG. 10, where both pumpsare off in a first operating condition;

FIG. 12 illustrates the valve arrangement of FIG. 10, where both pumpsare off in a second operating condition

FIG. 13 illustrates another ball valve arrangement showing conditionwith one pump on;

FIG. 14 illustrates the valve arrangement of FIG. 13 where both pumpsare off;

FIG. 15 is a front view of a delivery skid;

FIG. 16 is a side view of the delivery skid of FIG. 15;

FIG. 17 illustrates dual delivery skids assembled in parallel for use inthe systems of FIGS. 1 to 5.

DETAILED DESCRIPTION OF THE EMBODIMENT OR EMBODIMENTS

Illustrated in FIG. 1 is a schematic of a solar water heating system 10which comprises a primary circuit made up of a solar collector 11 (onlyone illustrated for ease of illustration—whereas a gang or bank of suchcollectors is normally used), a solar pump skid 12, heat transfer fluidtank 13 which serves as a drain back tank, and a delivery skid 14 (whichincludes a heat exchanger 14.1—only one illustrated for ease ofillustration—whereas a gang or bank 2 or more of such skids 14 can beused as described below in respect to FIGS. 15 to 17), and a potable hotwater delivery circuit or secondary circuit 15, which are all plumbedand connected together as described below.

The solar collection panel or collector 11 has an entry port 11.1 in itsbase and an exit port 11.2 at its top so that heated transfer fluid canexit the collector and via conduit 100 transfers to or makes it way tothe drain back tank 13. The collector 11 includes a temperature sensor11.3 which has its signals delivered to the controller 12.5 on the solarpump skid 12.

Delivering heat transfer fluid from the tank 13 to the collector 11 isthe function of the pump skid 12, which has a first pump 12.1 and asecond pump 12.2, which are of the non-displacement type such as animpeller type pump. The type of pump selected must be of the sort thatwill allow fluid to flow from the conduit 200 to the conduit 500 andback to the tank 13, if the pumps 12.1 and 12.2 are not operating. Thistype of pump is needed to ensure that the system 10 allows for the drainback of the heat transfer fluid from the collector 11 via conduit 200back through pump 12.1 and or 12.2 and then back to the tank 13.

The conduit 500 draws heat transfer fluid from the tank 13 from a lowerlocation thereon as the cooler heat transfer fluid is available fromsuch a lower location. Whereas, the heated transfer fluid exiting thecollector 11 via outlet 11.2 enters the tank 13 at an intermediateheight thereon, with the heated heat transfer fluid being drawn off viaconduit 300 from the top of the tank 13 for conveying to the inlet ofthe delivery skid 14. Whereas the conduit 400 returns the cooled heattransfer fluid which exits the heat exchanger 14.1 and conveys it backto the base of the tank 13, where it can be re-delivered to thecollector 11 via conduit 500, pump skid 12 and conduit 200.

The pump skid 12 has the parallel plumbed pumps 12.1 and 12.2 poweredfrom the control unit 12.5. The outlets of the pumps 12.1 and 12.2connect to the inlet ports on either side of a flap of a flap valve12.3, with the outlet of the valve 12.3 connecting to the inlet ofconduit 200. The construction of the valve 12.3 will be described inmore detail below with respect to FIGS. 6 to 10.

The pumps 12.1 and 12.2 are assembled with appropriate conduits each soas to be in parallel, so that should one pump fail, the other pump canbe operated. With suitable isolation valves, not illustrated, this willallow the replacement of the non-operating pump while the other pump isoperating.

In addition, the valve 12.3 is structured such that when the first pump12.1 is operating, while the outlet of the first pump 12.1 and theoutlet of said second pump 12.2 are connected to the valve 12.3, thenwhen the first pump 12.1 operates the outlet of the second pump 12.2 issubstantially closed due to the flow from the first pump 12.1 actingagainst the flap of the flap valve 12.3. Then and when the second pump12.2 operates—and pump 12.1 is not, the outlet of the first pump 12.1 issubstantially closed by the flow from the second pump 12.2 actingagainst the flap of the flap valve 12.3.

The valve 12.3 is arranged so that valve member or flap 12.37 of valve12.3 effectively closes a first pump 12.1 outlet port when the secondpump 12.2 is operating and the first pump 12.1 is not, and closes thesecond pump 12.2 outlet port when the first pump 12.1 is operating andthe second pump 12.2 is not operating.

The valve 12.3 as illustrated in FIGS. 6 to 10 comprises a valve body12.31 of brass or brass alloy (or any appropriate material), and inwhich is formed two ports 12.331 and 12.321 each respectively surroundedby a sealing rim 12.371 which when heat transfer fluid flows into thebody act as inlets to the valve 12.3. The two ports 12.331 and 12.321feed to the third port 12.341 which acts as an outlet when heat transferfluid flows out of the valve body and as an inlet when heat transferfluid flows into the valve body in a drain back condition.

It can be seen that the longitudinal axes 5 (normal to the plane of theports 12.331 and 12.321) are at 60 degrees to each other. This ensuresthat the pivoting or rotating flap 12.37 only rotates through 60 degreesfrom closing one port to closing the other port. The angle between thelongitudinal axes 5, being at 60 degrees, is not essential for theaction and or function of the flap 12.37. This measurement was selectedso that the angled valve seats 12.371 can be readily machined throughthe ports 12.331 and 12.321. The ports 12.331 and 12.321 could have beenlocated 180 degrees apart and the valve will function effectively

The flap 12.37 is made of stainless steel, and it will be noted thatnone of the flap 12.37 or the seats or sealing rims 12.371 include anypolymeric linings, mouldings or seats, and this makes the valve 12.3robust and relatively cheap to manufacturer which will give a goodservice life with little to no maintenance and very little risk offailure. While such mouldings are not necessary as a leak tight seal isnot required, this is not to say they couldn't be added if desired orrequired.

The flap 12.37 is of a circular configuration with a pivot tube 12.372at its base, which pivot tube 12.372 will sit in the part cylindricalsub housing 12.35 at the base of the valve body 12.31. The opposite endsof the pivot tube 12.372 on the flap 12.37 pivotally or rotatably holdthe flap 12.37 in the body 12.31 by interaction with opposed inwardlyextending pivot pins on the ends of machine screws 12.36. The heads ofthe respective machine screws 12.36 have a sealing washer (notillustrated) between the head and the sub housing 12.35 so that noleakage occurs in use.

The ports 12.321, 12.331 and 12.341 are each surrounded by femalethreaded hexagonal formation 12.32, 12.33 and 12.34, so that they canrespectively connect to the outlets of the pumps 12.1 and 12.2 and theinlet to conduit 200. While a female threaded connection is illustrated,it will be readily understood that any appropriate connection mechanismcan be utilised, including, amongst others, push fit connections, slipjoints, O-ring connections, male threaded connections, grooved couplingand grooved fittings such as those available under the Victualic brand,and any appropriate fitting mechanism.

The opposed side surfaces of the stainless steel flap 12.37 makescontact with the brass or brass alloy seats 12.371 to close therespective port of the other pump when a pump is running, however aperfect seal is not required, and as such no sealing components orpolymeric seats are used. While specific materials such as stainlesssteel for flap 12.37 and brass or brass alloy for the valve body 12.31and seats 12.371 are mentioned it will be understood that anyappropriate material for such components can be used including othermetals, polymeric materials or composite materials.

The valve 12.3 while one of the pumps 12.1 or 12.2 is operating closes areturn path for fluid which would otherwise go through the non-operatingpump. However the valve 12.3 also allows, when both pumps are notoperating, the ability for heat transfer fluid to drain back from theinlet 11.1 of the collector 11 back through the valve 12.3 and throughthe pump 12.1 or 12.6 depending on which side the flap 12.37 was restingagainst. So when one of the pumps is working its associated port invalve body 12.31 is an inlet, and the other pumps port is an outletwhich is closed off by the flap, and the third port which connects tothe conduit 200, is an outlet from the valve when a pump is operating,but is an inlet to the valve when the pumps are off.

In the FIGS. 1 to 4 there is illustrated check valves 12.4 locatedbetween the outlet of the pumps 12.1 and 12.2 and the valve 12.3.However, this is for representation purposes only, because from theprevious description it will be understood that the operation of onepump such as 12.1 ensures that the pumped flow, will not head towardsthe other pump, such as 12.2, because the pressure from pump 12.1 pushesthe flap 12.37 against the seat 12.371 on the inlet/outlet which leadsto or form the pump 12.2. With the opposite occurring when the pump 12.2is operated and the pump 12.1 is not.

It will be noted that the controller 12.5 in addition to receiving asignal from temperature sensor 11.3 also receives temperature signalsfrom sensors 13.1 at the bottom of the tank 13 and sensor 13.2 at thetop of the tank 13. Depending upon the temperatures available at the topsensor 13.2 the controller 12.5 can activate the electric element 13.3to boost the temperature of the heat transfer fluid in the tank 13.

The heat transfer fluid in the system described above can be anyappropriate heat transfer fluid which includes non-potable water or suchlike based liquids. However it will be understood that the heat transferfluid could also be potable water.

As illustrated in FIG. 1 the delivery skid 14 as mentioned aboveincludes a heat exchanger 14.1, which receives heated transfer fluidfrom the tank 13 in the primary circuit for the purpose of heatingpotable water in the heat exchanger 14.1 for the secondary circuit 15.The delivery skid 14 also includes two pumps 14.2 and 14.3 (the secondpump being available in case of failure of the first pump- or to sharethe load in an intermittent use modality) and two respective checkvalves 14.4, which in this instance, unlike valves 12.4, serve a checkvalve purpose. Heat transfer fluid transfers from tank 13 via conduit300 and exits the heat exchanger 14.1 and the delivery skid 14 back tothe tank 13 via the conduit 14.

On the secondary circuit side in the delivery skid 14, the conduit 600carries heated potable water from the delivery skid 14 to the end usersin this case represented by showering people icons 15.3. The secondarycircuit 15 includes a return conduit 700, a pump 15.2 and non-returnvalve 15.1 and conduit 800. At the end of conduit 800 the conduit 800enters a junction, a branch of which has incoming cold water supply viaa one way valve 15.4, and the other branch being conduit 900 to takeback cold water and return heated water to the heat exchanger 14.1 to bere-heated. Preferably in the delivery skid 14 there is also located aninline filter 14.5.

An important feature of the delivery skid 14 is that the control systemwhich operates the heat exchange fluid passing through the heatexchanger 14.1 measures the temperature at the outlet of the heatexchanger of the potable water circuit 15 by temperature sensor andsender 14.6, which is adjacent to an over temperature cut out 14.7. Inresponse to the temperature measured at sensor 14.6 the flow rate out ofthe pump 14.2 or 14.3 is increased so as to increase the temperature ofthe water at 14.6 or the flow rate is decreased to decrease thetemperature at the sensor 14.6. If the temperature cut out 14.7 isactivated the pumps 14.2 and or 14.3 can be switched off. Prior artsystems would otherwise use cold water mixing to obtain the desiredoutput potable water temperature.

Thus on the secondary side and the interface between the primary andsecondary sides, the water heating system 10 has a primary circuit tosupply a heated heat transfer fluid to the heat exchanger 14.1, whichsupplies heat to a secondary circuit 15 having potable water therein,wherein the primary circuit includes at least one pump 14.2 or 14.3 tocirculate the heat transfer fluid to and through the heat exchanger14.1, and a control system to control the operation and output flow rateof at least one pump 14.2 or 14.3, whereby the control system measuresthe temperature, or an indication of the temperature of said potablewater after it has left the heat exchanger 14.1 at location of sensor14.6, so as to control the output flow rate of the at least one pump14.2 or 14.3.

Illustrated in FIG. 2 is a water heating system 210, which is similar tothe system 10 of FIG. 1 and like parts and components have been likenumbered. The system 210 differs from the system 10, in that system 210does not include an indirect electric booster element 13.3 as part ofthe tank 13, but instead a direct booster in the form of a gas waterheater 15.5 is located between the outlet of the heat exchanger 14.1 andthe end users 15.3, on the end of conduit 600, and connects to the endusers 15.3 by intermediate conduit 650. The gas water heater 15.5 takesit signal to begin or cease operating from the solar pump skid 12's maincontroller 12.5, with potable water being pumped through the secondarycircuit 15 and water heater 15.5 by the pump 15.2.

Illustrated in FIG. 3 is a water heating system 310, which is similar tothe system 10 of FIG. 1 and like parts and components have been likenumbered. The system 310 differs from the system 10, in that system 310does not include an indirect electric booster element 13.3 as part ofthe tank 13, but instead a indirect booster in the form of a gas heattransfer fluid heater 13.5 which is located on the end of conduit 550which takes heat transfer fluid from tank 13 at an intermediate heightlocation on tank 13, and the heat transfer fluid exits heater 13.5 andre-enters the tank 13 at a high location via conduit 560 which has apump 13.6 controlled by the pump skid 2's main controller 12.5. The gasheat transfer fluid heater 13.5 takes it signal to begin or ceaseoperating from the solar pump skid 12's main controller 12.5.

Illustrated in FIG. 4 is a water heating system 410 which is similar tothat of system 310 of FIG. 3 and like parts and components have beenlike numbered. The system 410 differs from the system 310 in that a tankwired and controlled electric heating element 13.35 is present. Thesystem 410 is thus considered a hybrid system as it utilises one or acombination of more than one of the electric element 31.35, solarcollector 11 and or gas heater 13.5 to provide the heated transfer fluidin the tank 13. This hybrid system 410 can use energy from any one ormore of the solar, gas or electric inputs depending upon time ofoperation etc., so as to operate the system 410 as cost effectively asis possible with the mixture of three energy sources and the respectivetariffs and or costs associated with each.

Illustrated in FIG. 5 is a water heating system 510, which is similar toprevious systems in that a heat transfer fluid tank 13 is provided andwhich interacts with a delivery skid 14 with its heat exchanger 14.1like in other systems. Like parts and components have been likenumbered. The system 510 differs from previous systems in is that theprimary circuit is comprised of a co-generation unit 111 which utilisesa fuel via intake 111.2 such as natural or coal seam gas, which is burntin a burner/engine 111.5 with air induced from intake 111.3. The rotarymotion from engine 111.5 is used to rotate a generator 111.9, withelectricity fed to the building or grid via conductor 111.10. Thecombustion products from the engine 111.5 are fed, via a catalyticconverter 111.4 to a heat recovery heat exchanger 111.6 which heats heattransfer fluid to 80 to 95 degrees C. and which exits the unit byconduit 100 to be delivered to the tank 13. The cooled exhaust gassesexit the system via exhaust 111.8. When the tank has sufficient heatedtransfer fluid at the desired temperature, as electricity may need tocontinue to be generated, the excess heated transfer fluid is divertedback along conduit 160 where it is optionally combined with cooled heattransfer fluid from conduit 150, and is fed back to the co-generationunit, or if too hot still, is re-directed via valve 111.11 to conduit170 then to a chiller unit 111.12, and then back to the co-generationunit 111 via conduit 180 pump 111.7 and conduit 190.

Illustrated in FIGS. 10 to 12 is an alternative valve system 1230 whichis schematically illustrated as being plumbed in with pumps 12.1 and12.2. In the valve system 1230, the flap 12.37 of valve 12.3 of previousfigures is replaced by a ball 1237. The valve body 1231 has ports 12331and 12321 to which the outlets of the pumps 12.1 and 12.2 respectively.The third port 12341 would be connected to the conduit 200 for deliveryto, or receiving from, the collector 11. The ball 1237 is preferably ofstainless steel I (like flap 12.37) and the body 1231 of valve 120 ispreferably of brass or a brass alloy. As illustrated in FIG. 10, whenpump 12.2 is on, and pump 12.1 is off, the ball 1237 is pushed by theflow pressure from the pump 12.2 to push against the port 12331 and itsseat, thereby preventing a “short circuit” forming and forcing thepumped fluid to exit the valve 1230 via port 12341. If the pump 12.2 isthen switched off and pump 12.1 remains off, as in FIG. 11, then whenthe heat transfer is under gravity or under back pressure caused byoverheating in the collector 11 or freezing in the collector 11, thenthe heat transfer fluid can drain back through the port 12341 and thenport 12321 and back through pump 12.2 to the tank 13 via conduit 500. Asillustrate din FIG. 12, if the ball 1237 were to occupy an intermediateposition then heat transfer fluid can drain back through either or bothports 12331 and 12321 back through the pumps 12.1 and 12.2 and conduit500 to the tank 13.

As illustrate din FIGS. 13 and 14, a valve arrangement 123, similar tovalve arrangement 1230 is schematically illustrated, in the reversedconditions to FIGS. 10 and 11 above. The main difference between thevalve 123 and 1230 is that the valve 123 has its ports 1233.1 and 1232.1at the end of respective elbows in the valve body 123.1.

The valves 123 and 1230 as described above are illustrated in theirrespective figures with their third ports 1234.1 and 12341 in a verticalorientation on the page. However, it will be understood that they do notneed to be vertical when installed on the pump skid 12, as gravity doesnot adversely affect or influence the manner of operation of the valves123 and 1230.

As the units described above are meant for commercial water heatingsystems such as freshwater stations and or district water systems, thetanks 13 as represented in the FIGS. 1 to 5 are preferably of a mildsteel construction and are of a capacity of the order of 1000 to 5000litres, however any appropriate material can be used such as stainlesssteel, polymeric materials or composite materials such steel and enamellined tanks.

Illustrated in FIGS. 15 and 16 is a delivery skid 14, which has a base14.85 and upper structure 14.75 assembled thereon, which allows for themounting of two heat exchangers 14.1 which are connected in parallel tothe hot water supply conduit 600.1 at one end and to the ring mainreturn and cold water supply entry conduit 900.1 at the other end. Eachheat exchanger 14.1 connects in parallel to the conduits 600.1 and 900.1via a respective isolation valve 14.95. This allows the respective heatexchange 14.1 to be removed, replaced or repaired in the event of afailure, by simply closing isolation valve 14.95 related to the heatexchanger to be repaired or replaced, while at the same time opening thevalves 14.95 on the adjacent heat exchanger. Having this redundancy inthe delivery skid 14 ensures that there is no disruption to the supplyof heated water to the end users when a heat exchanger 14.1 needs to gooffline.

The conduits 600.1 and 900.1 each have respective flange 600.11 and900.11 at their respective ends, which as will be described later allowfor the connection to a like flange on an adjacent like delivery skid14. One flange end 600.11 and 900.1 will be blanked off by a flangedplate or cap 600.2 and 900.2, which thereby seals that end, in the casewhere a single skid 14 is employed in a system. The modular nature ofthe delivery skid 14 allows users to connect up as many as needed forthe hot water outputs required.

Also mounted on the base 14.85 and structure 14.75 are two pumps 14.2and 14.3 and respective isolation valves 14.95, and there are also checkvalves, filters sensors/senders, and temperature cut outs (item numbers14.4, 14.5, 14.6, 14.7 in FIGS. 1 to 5) which are not visible in FIG. 15or 16.

As illustrated in FIG. 17, two such delivery skids 14 are assembled sideby side, where one flanged plate 600.2 is used to close off one end ofthe conduits 600.1, and the flanged plated 900.2 to close off one end ofthe conduits 900.1. The number of skids 14 which would be connectedtogether to provide the assembly of delivery skids will be dependentupon the size of the system, the numbers of outlets and demand for hotwater in the buildings and or complexes where the water heating systemswill be installed.

As can be seen from FIG. 17, the primary flow of heat transfer fluid,the heat transfer fluid path being shown in broken line, passes into theskid 14 via the conduit 300, as in the other systems described above,which has an inline filter 14.5 and this path is split so as to entereach skid 14. This then passes to the pumps 14.2 and 14.3 as describedabove then to a respective the heat exchanger 14.1 (or both dependingupon needs) then exits the skid 14 back to the tank 13 via the conduit400.

The systems described above utilise a heat exchanger 14.1 and pumps14.2,14.3 to transfer energy in fluids to potable water at a useradjustable set point. Fluid that is heated by any means such aselectric, gas, cogeneration systems, solar systems, heat pumps etc isforced through heat exchangers 14.1 by pump 14.2, 14.3. The pumps 14.2,14.3 receive an electrical control signal from a temperature sensingdevice 14.6 (and cut off 14.7). By using a proportional integralderivative controller, the pump compares this control signal to its setpoint and the motors speed is altered accordingly. If the temperaturedetected is below the set point, the pump speeds up so as to flow morefluid through the heat exchangers 14.1. The effect of this higher fluidflow is a greater exchange of energy and therefore an increase in thetemperature of the potable water exiting the system and being deliveredto end users. Conversely if the energy required by the secondary side tomaintain a set temperature falls, the flow of fluid in the primary sidecontrolled by the pump also falls.

The temperature of the heat transfer fluid contained in a storage tank13 (see FIGS. 1 to 5) will rise and fall depending on its inputs andoutputs, for example an electric storage water heater's temperature willrise when it is heated by an immersion element and fall due to heat lossto the surroundings. The effect of a fall in the primary sidetemperature will be a reduction in the amount of energy exchanged withthe secondary side. This results in a fall in temperature on thesecondary side. The pump reacts to this fall in temperature byincreasing pump speed accordingly.

Flow rates on the secondary side will vary with user input.

The system can cope with very large fluctuations in temperature and floweither separately or simultaneously without altering the method ofcontrol.

The separation of fluid streams enables greater flexibility as thefluids need not be compatible with each other, for example cogenerationsystems using oil additives as the heating medium coupled with potablewater.

Due to the arrangement of components, the pressure drop across thesystem is very low which enables the use of highly efficiency pumpsoperating with very low energy input.

Upon failure of any sensing mechanism the systems will cease the flow offluid thus preventing any further exchange of heat. As such the systemshave a fail safe feature.

The systems do not require the addition of expensive valves insteadutilise a more intelligent version of a pump.

A solar system using heat transfer fluid on one side of the heatexchanger and potable water on the other is preferred, however it willbe readily understood that utilising alternative fluids, or even potablefluids, on both sides is an alternative.

The pumps 14.2 and 14.3 can be provided as either single headed or dualheaded versions to provide duty standby.

Illustrated in the FIGS. 1 to 5 are isolation valves which arerepresented

by the symbol and by item number 14.95 in FIGS. 15 to 17, and symbol

in FIG. 17. Such isolation valves generally appear at entries and exitsto components, where conduits are to be connected, and they allow forthe closing of such valves to assist in the removal and installation ofcomponents.

While the above description and embodiments are directed to potablewater systems, it will be readily understood that this invention andthese systems and components are able to be utilised with respect to theheating of other liquids other than potable water, such as milkprocessing plants and the like.

Where ever it is used, the word “comprising” is to be understood in its“open” sense, that is, in the sense of “including”, and thus not limitedto its “closed” sense, that is the sense of “consisting only of”. Acorresponding meaning is to be attributed to the corresponding words“comprise”, “comprised” and “comprises” where they appear.

It will be understood that the invention disclosed and defined hereinextends to all alternative combinations of two or more of the individualfeatures mentioned or evident from the text. All of these differentcombinations constitute various alternative aspects of the invention.

While particular embodiments of this invention have been described, itwill be evident to those skilled in the art that the present inventionmay be embodied in other specific forms without departing from theessential characteristics thereof. The present embodiments and examplesare therefore to be considered in all respects as illustrative and notrestrictive, and all modifications which would be obvious to thoseskilled in the art are therefore intended to be embraced therein.

1. A pump system for use with a solar collector system which is used toheat a heat transfer fluid, said solar collector system including astorage tank for said heat transfer fluid used in said solar collectorsystem, said pump system having a first and second pump arranged inparallel which can pump said heat transfer fluid from said storage tankto a solar collector, so that should one pump fail the other pump canfunction, wherein the outlet of said first pump and the outlet of saidsecond pump are connected to a valve arrangement, whereby when saidfirst pump operates the outlet of said second pump is substantiallyclosed by the flow from said first pump and when said second pumpoperates the outlet of said first pump is substantially closed by theflow from said second pump.
 2. The pump system as claimed in claim 1wherein said valve arrangement has three ports and a valve member whicheffectively closes a first pump's outlet port when a second pump isoperating and the first pump is not, and closes the second pump's outletport when a first pump is operating and said second pump is notoperating.
 3. The pump system as claimed in claim 2, wherein said threeway valve arrangement has a flap which closes said first pump's outletport and moves to a second location when activated by said first pump toclose said second pump's outlet port.
 4. The pump system as claimed inclaim 2, wherein said outlet ports are located on respective pipes whichconnect to said pumps.
 5. The pump system as claimed in claim 1, whereinsaid pump system is provided as part of a skid.
 6. A solar water heatingsystem having the pump system as claimed in claim 1 wherein said heattransfer fluid is not potable water.
 7. A solar water heating systemhaving the pump system as claimed in claim 1 wherein said heat transferfluid is potable water.
 8. A valve for a pump system having two pumpsand which will allow drain back of a pumped fluid, said valve includinga body having first and second ports for respectively connecting torespective pump outlets or conduits from said outlets, and a third port,whereby when a pump is pumping said third port is an outlet from saidbody, and when said pumps are not pumping, said third port is an inletto said body.
 9. The valve as claimed in claim 8, wherein between saidfirst and second ports a valve member can move so as to close off one ofsaid first or second ports depending upon which pump is operating. 10.The valve as claimed in claim 9, wherein said valve member is a flap.11. The valve as claimed in claim 10, wherein said flap is hingedlyconnected to said body which allows movement of said flap between saidfirst and said second ports.
 12. The valve as claimed in claim 8 whereinsaid valve closes off said first or second ports to a substantialextent, that is watertight sealing is not required by the valve.
 13. Thevalve as claimed in claim 10, wherein said flap is manufactured from ametal, polymeric material or composite.
 14. The valve as claimed inclaim 10 wherein valve seats surrounding said first and second ports aremanufactured from a metal, a polymeric or a composite material.
 15. Thevalve as claimed in claim 8, wherein surrounding said first port or saidsecond port or said third port is one of the following: a male thread, afemale thread.
 16. The valve as claimed in claim 8 wherein surrounding arespective port is a female thread.
 17. The valve as claimed in claim10, wherein said flap is held rotatable in said body, or pivotally heldin said body, by means of opposed pins which seal to said body and passinto said body.
 18. A water heating system having a primary circuit tosupply a heated heat transfer fluid to a heat exchanger, which suppliesheat to a secondary circuit having potable water therein, wherein saidprimary circuit includes at least one pump to circulate said heattransfer fluid to and through said heat exchanger, and a control systemto control the operation and output flow rate of said at least one pump,characterized in that said control system measures the temperature, oran indication of the temperature of said potable water after it has leftsaid heat exchanger, so as to control the output flow rate of said atleast one pump.
 19. The water heating system as claimed in claim 18,wherein said primary circuit heats the heat transfer fluid by one of ora combination of more than one of the following: solar; gas, electric,cogeneration means; gas boosted solar; electric boosted solar.
 20. Thewater heating system as claimed in claim 18, wherein said secondarycircuit has one or more of the following: is a freshwater stationsystem; is a district water heating system; includes a pump; includes afilter; includes a cold water supply; includes an over temperature shutdown mechanism.
 21. The water heating system as claimed in claim 18,wherein said heat exchanger is provided in a delivery skid whereby thereare two heat exchangers present on the skid, with respective isolationvalves and having parallel connections to an incoming conduit and anoutgoing conduit, whereby one of said heat exchangers is present in aredundancy capacity.
 22. The water heater system as claimed in claim 21,wherein said system can have multiple skids connected to each other toprovide the heat exchanger of the system.
 23. A heat exchanger apparatuscomprising a frame to support at least two heat exchangers, between aninlet conduit and an outlet conduit, wherein said at least two heatexchangers having connection to said inlet and outlet conduit inparallel, said connection being via isolation valves and forming aliquid supply inlet and heated liquid outlet, and each heat exchangerhaving fluid connection, via isolation valves, to a primary circuit toreceive a heat transfer fluid to transfer heat to said liquid,characterized in that at least one of said heat exchangers is present ina redundant capacity.
 24. The heat exchanger apparatus as claimed inclaim 23, wherein said inlet conduit and said outlet conduit haveflanged ends to allow connection to an adjacent like heat exchangerapparatus, and or a conduit closure.